There was a Sunday's New York Times article about that topic two weeks ago. It said that you often need to take a break from what you doing no matter how important a job. While this might seems waste of time to some, what you're actually doing is allowing your self to absorb the information you've just learned. Ideas come from all places. Archamedes came up with some of his ideas in the bath tub.
As for inspiration, most people set little or big goals for themselves if they feel like their work is going no where. I, for example, am going through with graduate school with the intention of buying a Porsche. Don't get me wrong I love what I'm doing (computer science). I also have days where I sit at night thinking what the hell I've been doing all these years and is what I'm doing making me happy.